This invention relates to methods of manufacture and devices useful in performing active biological operations. More particularly, the invention relates to devices containing active electrodes especially adapted for electrophoretic transport of nucleic acids, their hybridization and analysis.
Molecular biology comprises a wide variety of techniques for the analysis of nucleic acid and protein. Many of these techniques and procedures form the basis of clinical diagnostic assays and tests. These techniques include nucleic acid hybridization analysis, restriction enzyme analysis, genetic sequence analysis, and the separation and purification of nucleic acids and proteins (See, e.g., J. Sambrook, E. F. Fritsch, and T. Maniatis, Molecular Cloning: A Laboratory Manual, 2 Ed., Cold spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 1989).
Most of these techniques involve carrying out numerous operations (e.g., pipetting, centrifugations, electrophoresis) on a large number of samples. They are often complex and time consuming, and generally require a high degree of accuracy. Many a technique is limited in its application by a lack of sensitivity, specificity, or reproducibility. For example, these problems have limited many diagnostic applications of nucleic acid hybridization analysis.
The complete process for carrying out a DNA hybridization analysis for a genetic or infectious disease is very involved. Broadly speaking, the complete process may be divided into a number of steps and substeps (see FIG. 1). In the case of genetic disease diagnosis, the first step involves obtaining the sample (blood or tissue). Depending on the type of sample, various pre-treatments would be carried out. The second step involves disrupting or lysing the cells, which then release the crude DNA material along with other cellular constituents. Generally, several sub-steps are necessary to remove cell debris and to purify further the crude DNA. At this point several options exist for further processing and analysis. One option involves denaturing the purified sample DNA and carrying out a direct hybridization analysis in one of many formats (dot blot, microbead, microplate, etc.). A second option, called Southern blot hybridization, involves cleaving the DNA with restriction enzymes, separating the DNA fragments on an electrophoretic gel, blotting to a membrane filter, and then hybridizing the blot with specific DNA probe sequences. This procedure effectively reduces the complexity of the genomic DNA sample, and thereby helps to improve the hybridization specificity and sensitivity. Unfortunately, this procedure is long and arduous. A third option is to carry out the polymerase chain reaction (PCR) or other amplification procedure. The PCR procedure amplifies (increases) the number of target DNA sequences relative to non-target sequences. Amplification of target DNA helps to overcome problems related to complexity and sensitivity in genomic DNA analysis. All these procedures are time consuming, relatively complicated, and add significantly to the cost of a diagnostic test. After these sample preparation and DNA processing steps, the actual hybridization reaction is performed. Finally, detection and data analysis convert the hybridization event into an analytical result.
The steps of sample preparation and processing have typically been performed separate and apart from the other main steps of hybridization and detection and analysis. Indeed, the various substeps comprising sample preparation and DNA processing have often been performed as a discrete operation separate and apart from the other substeps. Considering these substeps in more detail, samples have been obtained through any number of means, such as obtaining of full blood, tissue, or other biological fluid samples. In the case of blood, the sample is processed to remove red blood cells and retain the desired nucleated (white) cells. This process is usually carried out by density gradient centrifugation. Cell disruption or lysis is then carried out on the nucleated cells to release DNA, preferably by the technique of sonication, freeze/thawing, or by addition of lysing reagents. Crude DNA is then separated from the cellular debris by a centrifugation step. Prior to hybridization, double-stranded DNA is denatured into single-stranded form. Denaturation of the double-stranded DNA has generally been performed by the techniques involving heating ( greater than Tm), changing salt concentration, addition of base (NaOH), or denaturing reagents (urea, formamide, etc.). Workers have suggested denaturing DNA into its single-stranded form in an electrochemical cell. The theory is stated to be that there is electron transfer to the DNA at the interface of an electrode, which effectively weakens the double-stranded structure and results in separation of the strands. See, generally, Stanley, xe2x80x9cDNA Denaturation by an Electric Potential,xe2x80x9d U.K. patent application 2,247,889 published Mar. 18, 1992.
Nucleic acid hybridization analysis generally involves the detection of a very small number of specific target nucleic acids (DNA or RNA) with an excess of probe DNA, among a relatively large amount of complex non-target nucleic acids. The substeps of DNA complexity reduction in sample preparation have been utilized to help detect low copy numbers (i.e., 10,000 to 100,000) of nucleic acid targets. DNA complexity is overcome to some degree by amplification of target nucleic acid sequences using polymerase chain reaction (PCR). (See, M. A. Innis et al, PCR Protocols: A Guide to Methods and Applications, Academic Press, 1990). While amplification results in an enormous number of target nucleic acid sequences that improves the subsequent direct probe hybridization step, amplification involves lengthy and cumbersome procedures that typically must be performed on a stand alone basis relative to the other substeps. Substantially complicated and relatively large equipment is required to perform the amplification step.
The actual hybridization reaction represents the most important and central step in the whole process. The hybridization step involves placing the prepared DNA sample in contact with a specific reporter probe, at a set of optimal conditions for hybridization to occur to the target DNA sequence. Hybridization may be performed in any one of a number of formats. For example, multiple sample nucleic acid hybridization analysis has been conducted on a variety of filter and solid support formats (See G. A. Beltz et al., in Methods in Enzymology, Vol. 100, Part B, R. Wu, L. Grossman, K. Moldave, Eds., Academic Press, New York, Chapter 19, pp. 266-308, 1985). One format, the so-called xe2x80x9cdot blotxe2x80x9d hybridization, involves the non-covalent attachment of target DNAs to filter, which are subsequently hybridized with a radioisotope labeled probe(s). xe2x80x9cDot blotxe2x80x9d hybridization gained wide-spread use, and many versions were developed (see M. L. M. Anderson and B. D. Young, in Nucleic Acid Hybridizationxe2x80x94A Practical Approach, B. D. Hames and S. J. Higgins, Eds., IRL Press, Washington, D.C. Chapter 4, pp. 73-111, 1985). It has been developed for multiple analysis of genomic mutations (D. Nanibhushan and D. Rabin, in EPA 0228075, Jul. 8, 1987) and for the detection of overlapping clones and the construction of genomic maps (G. A. Evans, in U.S. Pat. No. 5,219,726, Jun. 15, 1993).
New techniques are being developed for carrying out multiple sample nucleic acid hybridization analysis on micro-formatted multiplex or matrix devices (e.g., DNA chips) (see M. Barinaga, 253 Science, pp.1489, 1991; W. Bains, 10 Bio/Technology, pp. 757-758, 1992). These methods usually attach specific DNA sequences to very small specific areas of a solid support, such as micro-wells of a DNA chip. These hybridization formats are micro-scale versions of the conventional xe2x80x9cdot blotxe2x80x9d and xe2x80x9csandwichxe2x80x9d hybridization systems.
The micro-formatted hybridization can be used to carry out xe2x80x9csequencing by hybridizationxe2x80x9d (SBH) (see M. Barinaga, 253 Science, pp. 1489, 1991; W. Bains, 10 Bio/Technology, pp. 757-758, 1992). SBH makes use of all possible n-nucleotide oligomers (n-mers) to identify n-mers in an unknown DNA sample, which are subsequently aligned by algorithm analysis to produce the DNA sequence (R. Drmanac and R. Crkvenjakov, Yugoslav Patent Application #570/87, 1987; R. Drmanac et al., 4 Genomics, 114, 1989; Strezoska et al., 88 Proc. Natl. Acad. Sci. USA 10089, 1992; and R. Drmanac and R. B. Crkvenjakov, U.S. Pat. No. 5,202,231, Apr. 13, 1993).
There are two formats for carrying out SBH. The first format involves creating an array of all possible n-mers on a support, which is then hybridized with the target sequence. The second format involves attaching the target sequence to a support, which is sequentially probed with all possible n-mers. Both formats have the fundamental problems of direct probe hybridizations and additional difficulties related to multiplex hybridizations.
Southern, United Kingdom Patent Application GB 8810400, 1988; E. M. Southern et al., 13 Genomics 1008, 1992, proposed using the first format to analyze or sequence DNA. Southern identified a known single point mutation using PCR amplified genomic DNA. Southern also described a method for synthesizing an array of oligonucleotides on a solid support for SBH. However, Southern did not address how to achieve optimal stringency condition for each oligonucleotide on an array.
Concurrently, Drmanac et al., 260 Science 1649-1652, 1993, used the second format to sequence several short (116 bp) DNA sequences. Target DNAs were attached to membrane supports (xe2x80x9cdot blotxe2x80x9d format). Each filter was sequentially hybridized with 272 labeled 10-mer and 11-mer oligonucleotides. A wide range of stringency condition was used to achieve specific hybridization for each n-mer probe; washing times varied from 5 minutes to overnight, and temperatures from 0 C. to 16 C. Most probes required 3 hours of washing at 16 C. The filters had to be exposed for 2 to 18 hours in order to detect hybridization signals. The overall false positive hybridization rate was 5% in spite of the simple target sequences, the reduced set of oligomer probes, and the use of the most stringent conditions available.
A variety of methods exist for detection and analysis of the hybridization events. Depending on the reporter group (fluorophore, enzyme, radioisotope, etc.) used to label the DNA probe, detection and analysis are carried out fluorimetrically, colorimetrically, or by autoradiography. By observing and measuring emitted radiation, such as fluorescent radiation or particle emission, information may be obtained about the hybridization events. Even when detection methods have very high intrinsic sensitivity, detection of hybridization events is difficult because of the background presence of non-specifically bound materials. A number of other factors also reduce the sensitivity and selectivity of DNA hybridization assays.
In conventional fluorimetric detection systems, an excitation energy of one wavelength is delivered to the region of interest and energy of a different wavelength is remitted and detected. Large scale systems, generally those having a region of interest of two millimeters or greater, have been manufactured in which the quality of the overall system is not inherently limited by the size requirements of the optical elements or the ability to place them in optical proximity to the region of interest. However, with small geometries, such as those below 2 millimeters, and especially those on the order of 500 microns or less in size of the region of interest, the conventional approaches to fluorimeter design have proved inadequate. Generally, the excitation and emission optical elements must be placed close to the region of interest. Preferably, a focused spot size is relatively small, often requiring sophisticated optical designs. Further, because it is usually desirable to maximize the detectable area, the size of the optical components required to achieve these goals in relation to their distance from the region of interest becomes important, and in many cases, compromises the performance obtained. Accordingly, a need exists for an improved fluorescent detection system.
Attempts have been made to combine certain processing steps or substeps together. For example, various microrobotic systems have been proposed for preparing arrays of DNA probe on a support material. For example, Beattie et al., in The 1992 San Diego Conference: Genetic Recognition, November 1992, used a microrobotic system to deposit micro-droplets containing specific DNA sequences into individual microfabricated sample wells on a glass substrate.
Generally, the prior art processes have been extremely labor and time intensive. For example, the PCR amplification process is time consuming and adds cost to the diagnostic assay. Multiple steps requiring human intervention either during the process or between processes is suboptimal in that there is a possibility of contamination and operator error. Further, the use of multiple machines or complicated robotic systems for performing the individual processes is often prohibitive except for the largest laboratories, both in terms of the expense and physical space requirements.
As is apparent from the preceding discussion, numerous attempts have been made to provide effective techniques to conduct multi-step, multiplex molecular biological reactions. However, for the reasons stated above, these techniques are xe2x80x9cpiece-mealxe2x80x9d and limited. These various approaches are not easily combined to form a system which can carry out a complete DNA diagnostic assay. Despite the long recognized need for such a system, no satisfactory solution has been proposed previously.
Methods of manufacture and apparatus adapted for advantageous use in active electronic devices utilized for biological diagnostics are disclosed. In the preferred embodiment, a multilayer, laminated device includes at least a first planar sample support, the planar sample support including a through hole, a planar electrode adjacent the planar sample support, the electrode including a through region, and a second planar support including a vent through hole, the planar electrode being in a laminated relationship between the first planar sample support and the second planar support, further characterized in that the sample through hole, electrode through region and vent through hole overlap one another. In the preferred embodiment, the planar support members may be formed of a thin, sheet-like material, most preferably a polyimide sheet such as DuPont Kapton. The preferred thickness of a planar support is in the range from 1 to 5 mils. The planar sample support material is advantageously selected to have properties consistent with the goals and purposes of the active biological device, for example, exhibiting low binding properties for DNA, having low inherent fluorescence, being relatively inert in an acidic environment and being nonconducting.
Stacked or laminated structures may be formed through the use of multiple sheets. In one preferred embodiment, one or more additional layers are disposed above the planar sample support in a direction towards the surface, which will receive the biological material. Similarly, a multilayer or laminated structure may be formed beneath the second planar support. The additional laminated layers would typically include through holes, which preferably would be aligned with the remaining through holes or regions. Multilayer or laminated structures may be advantageously formed in numerous configurations. In one embodiment, electrodes may be disposed at differing depths relative to the sample side of the laminated device such that different offset distances between the electrode and the sample applied to the device are achieved. In this way, the different offset distances permit optimization of various functions, such as where complexity reduction and assaying are performed on the same device. Electrodes may be formed at different levels such as through use of an intervening planar support disposed between a first electrode and a second electrode at different levels.
In one aspect of this invention, the lateral dimension of the through hole of the first planar sample support is different than the lateral width of the vent through hole of the second planar support. In one embodiment, the lateral dimensions of the vent through hole are larger than the lateral dimensions of the sample through hole. Preferably, a permeation layer is included in the sample through hole and at least a portion of the vent through hole. Relative advantages of this embodiment potentially include the advantageous venting of gas from reactions at or near the planar electrode through a region separate from the hybridization reaction, and the ability of this structure to lock in a permeation layer disposed in the sample through hole, electrode through region and at least a portion of the vent through hole. An alternative embodiment has a sample through hole with a lateral dimension, which is greater than the lateral dimension of the vent through hole. The planar electrode includes at least a portion oriented to face outward through the sample through hole.
In another aspect of this invention, fluidic devices may be formed on, within, or adjacent to the laminated structures. For example, a pump, such as a magnetically driven microminiature pump may be included within the laminated structure. Fluids may be pumped or moved through the system in such a manner.
In yet another aspect of this invention, chip-on flexible circuit technology may be employed to hybridize electronic circuitry in operative contact with the active biological device. Further, multiple level interconnections may be formed, such as through use of vias connecting between one or more layers. In the preferred embodiment, these vias may be exposed to external of the device through the second planar support, rather than through the uppermost planar sample support which adapted to receive biological materials.
The laminated circuit structures and methods of this invention are advantageously utilized in forming active biological devices. A device having a combination of biological complexity reduction and diagnostic assay, as well as counter electrodes may be formed on a single device.
In yet another aspect of this invention, a multilayer, laminated structure may be utilized to perform biological amplification processes, especially polymerase chain reaction (PCR). Optionally, one or more heaters may be integrated into or formed adjacent the laminated structure to aid in the amplification process.
Accordingly, it is an object of this invention to provide an active biological device having reduced costs of manufacture yet consistent with achieving a small size microlocation.
It is yet another object of this invention to provide a device having a high degree of uniformity of exposed electrode from microlocation to microlocation, as well as device to device.
It is yet a further object of this invention to provide a active biological device having reduced bubbling and reduced burn-out.
It is yet another object of this invention to provide an active biological device having improved gas venting and buffering capacity.